XxXJ99xX

Alright so this is now my fourth cherokee and I have to say out of all of the XJ's I've owned it is by far the worst on gas millage hands down. I recently added a brand new exhaust, O2 sensor, Accel Tune up kit, K&N air filter and changed my diff fluids and also had the rear end completely rebuilt. Before I was getting around 11 mpg's. After all of that work I am only getting 15.5 mpg now, it is an Autotragic with the 4.0 and 3.73's with 235's. I am trying to find some sort of explanation for all of this because It seems like I have checked over almost everything in the jeep and I have some ideas but I would still like to know if anyone had these problems and have found a solution. I would be outside checking everything over right now but the 15 degree weather with gusting winds in an open parking lot is preventing that. Any help is appreciated and thanks in advance guys

ZINGGG

I assume you changed motor oil and oil filter already? Also, fuel filter, clean throttle body, run seafoam through the gas tank and brake booster vacuum line. By new exhaust, did you replace from the manifold back? If you just went cat-back, I would check for a cracked manifold

If you have any sort of lift or bigger tires, 15 is pretty dang good! But since you are pretty much stock, you should be getting a little better than that...

XxXJ99xX

I changed the motor oil around 4000 miles ago with Mobil 1 Extended Guard, some Lucas oil additive and a K&N Oil Filter. Fuel filter is in the gas tank on Cherokees in the form of a sock for the pick up tube. I already have ran seafoam through the gas tank and through the brake booster line, I ran it from the cat back because it blew the O2 sensor through the cat and there were holes the whole way back. The manifold is cracked I believe or the exhaust manifold gasket is gone. I have had cracked manifolds in cherokees before and never really had them effect gas millage...At least I dont think. I'm on stock lift and one size above stock tires. I was getting 22 in my 99 Auto...

ZINGGG

Sounds like it's time for a replacement. I would think that'd have a lot to do with your mpgs being so low. I remember reading that a guy had a cracked manifold, replaced it and saw an improvement of 5 MPGs. Mine is cracked at the moment and I'm getting around 10 (granted I'm lifted with 33s) so I'm hoping for a small improvement once I replace it.

Heard very good things about the APN:
http://www.ineedparts.com/auto-parts...-manifold.html

XxXJ99xX

That looks like a well constructed manifold and I'd love to order it but I dont have the money or time to do it at all. I'll do alittle more investigation on what it could be but im defiantly not ruling it out. Are there any sensors or anything else that could be causing it?

Firestorm500

3.73 gears are letting your RPM's get a little high on the highway. Could be hurting your mileage a little bit.

15.5 MPG is about average. Winter blend fuels that have more O2 added could cause a little drop.

Next time, leave out the Lucas. Thicker oil leads to MPG losses. Mobil 1 10W-30 and a good filter is all you need.

XxXJ99xX

Thats what I would've assumed but it isnt running much higher then stock, and It was 15.5 mpg for a month before it started to get truly cold and winter blend was switched out. The only reason I put in the lucas is because I planned on not changing the oil for 6000 miles and wanted the be sure my 4.0L was protected. I'm extremely religious on my oil changes and services so I've never gone over 3000 and the lucas just made me feel better.

88CherokeeKid

I would say that 15 almost 16 is pretty good, I mean the thing is 4 liters!